This invention relates to an automatic operating system of a machine tool and method, more particularly to a system and method of operation for exchanging a tool and a workpiece worked thereby when the tool breaks or wears.
In an automatic operating system of a machine tool wherein a plurality of different workpieces are machined sequentially over a long time by using machine tools including a plurality of machining centers, there are many problems to be solved including
(a) handling of the chips, PA1 (b) detection of the presence or absence of a workpiece to be supplied, that is the detection of a pallet which carries the last workpiece and deenergization of the system, PA1 (c) detection of the abnormal cutting of each machine tool and the operation of the control system after the detection, and PA1 (d) administration of the cutting agent.
Among these problems, (c) is the most important for performing an automatic operation. When abnormal cutting occurs various expedients have been used for the purpose of preventing the shut down of the entire system or a specific machine tool in which abnormal cutting is detected.
Suppose now that while a machining center (MC) is machining an opening through a workpiece for tapping, a drill for machining the opening breaks. Even when the breakage is detected by some detecting means, continued machining of the opening by a new drill is not possible because fragments of the broken drill remain in the opening. In such a case, it is not simple to automatically check whether the fragments of the drill remain in the opening or not and to remove the remaining fragments.
According to another proposed method, the drilling operation is interrupted and the workpiece is advanced to another working position without completing the drilling operation. Where a plurality of openings for tapping are to be formed by the same drill, it is usual to sequentially form the openings and then successively form screw threads with a tap. Accordingly, when a drill breaks while it is being used to form an opening for tapping at a given position (X.sub.j, Y.sub.j, Z.sub.j), a new identical drill is used to sequentially form openings at other working positions, and then screw threads are formed by using a tap, it is necessary to avoid to use the tap at said position (X.sub.j, Y.sub.j, Z.sub.j). More particularly, while a working program is being executed, when an accidental fault, for example breakage of a tool T.sub.1 occurs at a working position (X.sub.j, Y.sub.j, Z.sub.j), to instruct that the working by a different tool T.sub.2 at the same position should be eliminated while executing a subsequent working program, and to store said working position complicates the construction and operation of the control system.
Where K working steps are required to machine a workpiece at a given position (X.sub.j, Y.sub.j, Z.sub.j), when the fault occurs in the first working step it is necessary to modify an NC (numerically controlled) program so as to omit remaining (K-1) working steps at that position, thus complicating the NC system. Such modified control is based on the desire that even when a portion of the working step is not performed it is desirous to perform as far as possible the remaining steps.